Apple requires all third-party apps that sync with iCloud (like BusyCal and BusyContacts) to use app-specific passwords - your standard iCloud password will not work. An app-specific password is essentially a 19 character long (separated by dashes), custom password generated by Apple that is different than your standard iCloud password. Only Apple's apps (Mail, Calendar and Contacts) can use your standard iCloud password. All other apps must use an app-specific password to connect with your iCloud account.